It looks like the RX 5700 XT with the latest driver (19.9.2, 19.9.3) do not react on texture LOD bias (GL_TEXTURE_LOD_BIAS) param. We have a number of GPUs, both AMD and Nvidia here in CI rack. Since we have got the RX 5700 XT it has produced slightly different renderings, so after tracking down the problem it is obvious that LOD bias has no effect on this GPU. Without setting LOD bias all GPUs including RX 5700 XT give the same results. With LOD bias set RX 5700 XT still samples textures on an unbiased mip level.
I wonder if it is a known issue or not yet. Before I start creating a repro case for dedicated bug report...